Abstract
We investigated spin-orbit torques in prototypical Pt-based spintronic devices. We found that, in Pt/Ni and Pt/Fe bilayers, the damping-like torque efficiency depends on the thickness of the Pt layer. We also found that the damping-like torque efficiency is almost identical in the Pt/Ni and Pt/Fe bilayers despite the stronger spin memory loss at the Pt/Fe interface. These results suggest that although the dominant source of the damping-like torque is the bulk spin Hall effect in the Pt layer, a sizable damping-like torque is generated by the interface in the Pt/Fe bilayer due to the stronger interfacial spin-orbit coupling. In contrast to the damping-like torque, whose magnitude and sign are almost identical in the Pt/Ni and Pt/Fe bilayers, the field-like torque strongly depends on the choice of the ferromagnetic layer. The sign of the field-like torque originating from the bulk spin Hall effect in the Pt layer is opposite between the Pt/Ni and Pt/Fe bilayers, which can be attributed to the opposite sign of the imaginary part of the spin-mixing conductance. These results demonstrate that the spin-orbit torques are quite sensitive to the electronic structure of the FM layer.
Highlights
Current-induced spin-orbit torques provide a promising strategy for the electrical manipulation of magnetization in metals, semiconductors, and insulators [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
These results suggest that the dominant source of the dampinglike torque is the bulk spin Hall effect in the Pt layer, a sizable dampinglike torque is generated by the interface in the Pt/Fe bilayer due to the stronger interfacial spin-orbit coupling
We find that the sign of the fieldlike torque originating from the bulk spin Hall effect in the Pt layer is opposite between the Pt/Ni and Pt/Fe bilayers, which can be attributed to the opposite sign of the imaginary part of the spin-mixing conductance
Summary
Current-induced spin-orbit torques provide a promising strategy for the electrical manipulation of magnetization in metals, semiconductors, and insulators [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. In the HM/FM bilayer, the angular momentum carried by the spin Hall current is transferred to the magnetization through the spin-transfer mechanism [1] This angular momentum transfer induces a torque on the magnetization, which is expressed as τDL = τDLm × (σ × m), where m is the magnetization unit vector, σ is the unit vector along the spin-polarization direction of the spin current, and τDL is the magnitude of the torque. The torque of this form is referred to as a dampinglike torque.
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